With development and application of a 4G-LTE technology, antenna bandwidth of a terminal product needs to cover more frequency bands. According to a user demand on portability and aesthetic appeal of the product, an antenna is required to occupy as little space as possible. However, miniaturization and broadband are in contradiction. Therefore, in such a background, a tunable antenna becomes one of trend technologies to resolve the contradiction problem. The tunable antenna means that different inductance components or capacity components are mounted to a “sensitive position” of the antenna, or a switch between connection and disconnection is implemented, so as to change an impedance characteristic of the antenna. The foregoing “sensitive position” mainly includes an excitation point of the antenna, a ground point of the antenna, a wire of an antenna body, or the like.
In an existing tunable antenna, a tunable component such as a switch component is connected in series to a ground point of the antenna; a back end of the switch component is connected to an inductor or a capacitor that varies in inductance or capacitance, and is then connected to the ground. After the tunable component is connected in series, switching between “a state of multiple inductors, a state of multiple capacitors, and a state of directly connection to the ground” may be performed according to an antenna design requirement. With switching of the switch, a ground point is connected to different components, and an impedance characteristic at an excitation point is correspondingly affected; therefore, a change in an operating frequency band of the antenna may be implemented. Finally, a sum of frequency bands that can be covered in multiple change states is total bandwidth that the tunable antenna can finally cover.
In the prior art, bandwidth of an antenna at a low frequency is extended by using a tunable component. Though an operating frequency band of the antenna at the low frequency changes as expected when each tunable component switches or changes, a frequency response of the antenna in a high frequency band also changes accordingly after each tunable component switches or changes or when the tunable component is in each operating state, and the change at a high frequency is generally irregular.